Comparative study of the electrochemical and pulse-radiolytic oxidation of the complexes of nickel(II) and copper(II) containing 1,4,8,11-tetra-azacyclotetradecane

Abstract

Electrochemical and pulse-radiolytic oxidation of [ N i ( c y ~I a m ) ] ~+ and [Cu(cyclam)12+ (cyclam = 1,4,8,11tetra-azacyclotetradecane) have been studied in aqueous acidic perchlorate and sulphate media. As with other nickel macrocyclic systems, [ N i ( c y ~I a m ) ] ~+ is oxidized to Ni*'I, the stability of which is enhanced by sulphate complexation. In contrast, [Cu(~yclam)]~+ is much less stable than the nickel analogue and does not form a stable sulphate complex. Electrochemical oxidation of [Cu(cyclam)12+ at pH 1.6 is a multistep process which is catalysed by sulphate ion. The mechanism appears to involve the transfer of four electrons resulting in a copper(t1) macrocyclic diene complex.

Macrocyclic ligand design. Interaction of a series of successively N-benzylated derivatives of 1,4,8,11-tetraazacyclotetradecane (cyclam) with copper(ii) and nickel(ii)

“…The value obtained for the corresponding nickel complex of cyclam, [Ni(6)] 2ϩ , is 459 nm. This cation 12,13 has been well documented to be square planar in both the solid state 14,15 and (in the absence of coordinating anions) also in aqueous solution; 16 in the latter solvent the absorption maximum in the visible region occurs at 450 nm (ε = 45 M Ϫ1 cm Ϫ1 ).…”

“…The residue was recrystallized from a mixture of dichloromethane and methanol to yield red-purple crystals (0.30 g, 60%). Single crystals suitable for X-ray diffraction were obtained from dichloromethane-methanol (1 : 1) (Found: C, 42.68; H, 6.70; N, 16.89. C 17.5 H 32 CuN 6 O 6.5 requires C, 42.55; H, 6.53; N, 17.01%).…”

Electron Exchange Columns through Entrapment of a Nickel Cyclam in a Sol–Gel Matrix

“…6 relatively fast in a second-order process. [12][13][14] In order to inhibit the last reaction it seemed that the preferred route of preparing the column is by the sol-gel entrapment procedure.…”

Mechanism of Isomerization of Ni(cyclam) in Aqueous Solutions

“…As sulfate was shown to stabilize [Ni III (L i )] 3+ ( i = 1, 2, 7),22,23,27,28 it seemed of interest to investigate the difference in behaviour of the two [Ni III (cyclam)] 3+ isomers. CV and square‐wave experiments showed that the trans ‐ III ‐[Ni III (cyclam)] 3+ isomer as expected for the relative symmetrical octahedral environment, binds two sulfate anions (Figure 5) with K = 2 × 10 6 M –2 , the CVs are reversible.…”